1. Field of the Invention
This invention relates to crosslinked polymers of vinyl pyrrolidone, and, more particularly, to such polymers which contain a crosslinker having both a pendant divinyl moiety and a chelation group capable of complexing with and removing heavy metal ions from aqueous solutions, particularly wine and beer.
2. Description of the Prior Art
The term "popcorn" or "proliferous" polymerization was introduced to define a well-known phenomenon, when, in an originally homogeneous liquid monomer, heterogeneous polymer nuclei appear, and there further growth rate becomes predominant. When a certain amount of popcorn polymer is isolated from the reaction mixture and added to the fresh portion of monomer, this polymer is able to continue its propagation and give rise to further development of the popcorn polymer. See C. H. Bamford, et al., "The Kinetics of Vinyl Polymerization by Radical Mechanisms", Butterworths Scientific Publications, London, 1968.
A water-insoluble polymer product of popcorn polymerization is crosslinked polyvinylpolypyrrolidone (PVPP), which has been made by proliferous polymerization of vinyl pyrrolidone (VP). The process may be carried out in the absence of added crosslinker, or in the presence of an added crosslinking agent, or with an in situ generated crosslinker. Such crosslinking polymerization processes are described in U.S. Pat. Nos. 3,277,066; 3,306,886; 3,759,880; 3,933,766; 3,992,562; and 5,094,867; and in an article by F. Haaf et al. in Polymer J. 17(1), p. 143-152 (1985), entitled, "Polymers of N-Vinylpyrrolidone:Synthesis, Characterization and Uses".
PVPP polymers are widely employed as clarifying agents in the industrial purification of aqueous wine and beer solutions, particularly for the removal by adsorption of organic impurities such as polyphenols, tannins and anthracyanins which may be present in the aqueous solution. As a result of such treatment, a clear, haze-free wine or beer product may be obtained. However, this polymer is incapable of adsorbing heavy metal ions, in particular, copper and iron ions, which also contribute to the cloudiness of such solutions.
Preferably, methylene bis-acrylamide is used as the crosslinking agent for preparation of PVPP. In this case, the synthesized polymer is characterized by well-pronounced adsorption properties with respect to polyphenols, and this offers substantial advantages for its practical application.
Controlled modification of the properties of PVPP may be accomplished by the introduction of comonomers with vinyl pyrrolidone which contain functional or ligand groups capable of preferential binding of copper or iron ions. For example, U.S. Pat. 5,094,867 described the use of 50-99.5% of a ligand-containing comonomer, particularly, N-vinylimidazole, an amine-containing comonomer, in combination with vinyl pyrrolidone, was described. However, no crosslinking agents have been developed which are able to complex strongly with copper ions.
Accordingly, it is an object of this invention to provide new and improved polyvinylpolypyrrolidone (PVPP) polymers for use in the industrial clarification of wine and beer which will also remove traces of heavy metal cations therein.
Another object herein is to provide crosslinked PVPP polymers including a crosslinker which contains a chelation group in the molecule capable of complexing effectively with a heavy metal ion such as copper or iron in aqueous solution.
Yet another object herein is to provide a crosslinker compound containing a pendant divinyl moiety and a group capable of chelating with heavy metal ions, for use in polymerization of vinyl pyrrolidone to form a new and improved crosslinked PVP.
Still another object herein is to provide a proliferous polymerization process for making such crosslinked polymers of vinyl pyrrolidone.
Among the other objects herein is to provide a process of clarifying an aqueous solution of wine or beer by treatment with a crosslinked polymer of vinyl pyrrolidone monomer and a crosslinker compound containing both a pendant divinyl moiety and a group capable of chelating with a heavy metal ion in aqueous solution.
These and other objects and features of the invention will be made apparent from the following more particular description of the invention.